Surround Suppression

back to wadelab home: research overview

      Contrast is the fundamental currency of the early visual system. The perceived contrast at a particular spatial location depends both on the local rate of photon absorptions in the retina and also on the contrast in other parts of the visual field. In recent years, it has become clear that these long-range interactions are tuned for a variety of spatiotemporal properties including orientation, direction and spatial frequency and that they transfer across eyes. This, in turn, indicates that long-range interactions arise in cortex (where spatiotemporal tuning is strong) rather than in sub-cortical structures such as the retina or lateral geniculate nucleus (LGN).

One of the best-studied long-range interactions is an effect known as ‘surround suppression’. This refers to the reduction in apparent contrast of a low-contrast ‘probe’ region when it is placed in proximity to a high-contrast ‘surround’. We measure the orientation and contrast-dependence of surround suppression using both high-density, source-imaged EEG and psychophysics. Our source-imaging techniques allow us to localize scalp-EEG measures to cortex at the resolution of individual visual areas, and to probe the neural dynamics of surround suppression in humans using extremely accurate temporal measurement.